This invention relates to a method of forming semiconductor devices. More particularly this invention relates to a semiconductor substrate processing method for selectively forming different conductivity region at predetermined positions.
The integrated-circuit manufacturing technique forming a large number of elements on a single substrate has greatly been advanced. As one of methods for forming increased number of active elements per unit area of a semiconductor substrate, the local oxidation of silicon (LOCOS) method is well known. In this method a silicon nitride layer is formed on a selected portion of the silicon substrate and the remaining area is oxidized. After removing the silicon nitride layer, the position is then diffused with impurities thereby forming one conductivity type of region, which is used as the base. In the conductivity region is formed another type of conductivity region to be used as the emitter. Comparing the method of LOCOS with the prior art of planar semiconductor device forming method, the LOCOS has the advantage of eliminating a process of mask alignment for etching. However, the LOCOS method requires high heat treatment, which lowers the reliability and productivity of semiconductor devices.